Astronomers solve the mystery surrounding galaxy bulges

The Milky Way galaxy looks like a flat disc, but gamma ray emissions show that it has two bulging discs coming out of it called Fermi Bubbles. They are result of the supermassive black hole eating in the center of the galaxy. With the help of Hubble telescope, astronomers found out how this structure was created.

Hubble and quasars

 

Rongmon Bordoloi from the Massachusetts Institute of Technology led a team to trace the structure and motion of the northern Fermi Bubble using distant quasars. The northern bubble rises 23,000 light years above and has the mass of 2 million suns. They observed 47 quasars and mapped out the cool gas and found out its age – 6 to 9 million years.

 

Many galaxies contain supermassive black holes. Our galaxy Sag A* weight at 4,5 million solar masses and its rotation has slowed down. In stark contrast, quasars are young black holes that suck massive amounts of gas and dust and shine brightly while the material goes into the accretion disk and the it is “eaten” by the black hole.

Astronomers believe that Sag A*  was pretty much like those young black holes in the early universe.

 

However, sometimes the material is not engulfed by the black hole and it is shot at tens of thousands light years. The Fermi Bubbles of our galaxy are such an outflow. They are named after the telescope that found them – the Fermi Gamma-Ray Telescope.

The motion of interstellar gas

To find out more about the origins of such outflows we need to study their motion. “We have traced the outflows of other galaxies, but we have never been able to actually map the motion of the gas,” said Bordoloi when he announced his group’s results. “The only reason we could do it here is because we are inside the Milky Way. This vantage point gives us a front-row seat to map out the kinematic structure of the Milky Way outflow.”

 

When the light from quasars travel thru the bubble, its highlights the gas in it. This allows the astronomers to find its chemical composition, motion and temperature. The gas from the Northern Fermi Bubble contains elements like carbon and silicon. It speed was clocked at 2 million miles per hour (3,2 million kph), and reaches scalding hot temperatures of 17,000 degrees Fahrenheit.

 

This gas is likely from the disk of the galaxy that has been swept and combined with the outflow. It can reach temperatures of 18 million degrees Fahrenheit (10 million Celsius). Because of the high temperatures, the gas shines brightly much like the gamma rays.

 

When researchers found out the gas motion, they used this data to pinpoint the time when it “erupted” from the black hole.


“What we find is that a very strong, energetic event happened 6 million to 9 million years ago,” Bordoloi explained. “It may have been a cloud of gas flowing into the black hole, which fired off jets of matter, forming the twin lobes of hot gas seen in X-ray and gamma-ray observations. Ever since then, the black hole has just been eating snacks.”

Source: Astronomy.com